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Dive, Dive!

In films, a hero often evades bullets by jumping into a river or lake. How far below the surface do they need to dive?

• Any object moving through a medium experiences a drag force tending to slow it down. For a denser medium like water, the drag force is much larger than it is in air. Water is 700 times denser than air. The drag force on the bullet scales as the square of the velocity and is also proportional to the surface area of the moving body.